1. Field of the Invention
The present invention relates generally to glass breakage detection, communication devices, and security systems. More particularly, the invention pertains to an apparatus and method for calibrating a glass breakage detection system that includes an impact sensor mounted on the glass window or door to detect a physical/mechanical impact to the glass window or door and an acoustic sensor for confirming that the glass is broken by detecting a sound of breaking glass of a glass window within a predetermined time period. An alarm is only generated if both detections occur within the time period.
2. Discussion of the Prior Art
The present invention addresses the commercial problem of a security system, such as a commercial or residential/home security system, providing a glass breakage sensor for detecting an intrusion into a protected space through a glass window or door. Acoustic detectors are commonly used to detect and indicate attempts to break into a premises by breaking glass objects. The detector generates an alarm signal when the sound of breaking glass windows or glass doors is detected. Typically, the detectors are remotely mounted from the protected glass and are attached to a ceiling or a wall. The location of the detector is dependent on the size of the protected area.
The detectors rely on detecting the sound of breaking glass by sensing one or more known frequency components associated with the sound of breaking glass. When the glass break detector is installed, it is typically tested to ensure proper functionality. The detection is tested such that the acoustic properties of the environment are compensated for by a sensitivity adjustment to optimize the sensing range of the detector. However, even with this adjustment, false alarms can be generated by sounds other than those of breaking glass from a glass window or door that can fool the audio processor and cause the issuance of a false alarm by the security system. Some examples of sounds that can fool the audio processor and cause the issuance of false alarms include sounds of a barking dog, the popping of a balloon, a dropping of a pot or pan, an accidental dropping and breakage of a drinking glass, and the closing of a kitchen cabinet.
To avoid false alarms an impact detector is used to detect vibrations on a window. An alarm is only generated if both the acoustic sensor detects the sound of breaking glass and an impact sensor on the glass window or door detects a physical/mechanical impact to the glass window or door. Still false alarms can be generated if both sensors detect an “event”, but the detection is separated by a period of time. Further the time between the detection of the impact and the detection of the breaking glass will vary dramatically in different environments, temperatures, altitudes and size of a premise.
Additionally, various common objects found in an indoor location can negatively affect the performance of the detector and time between the detection, such as carpet, ceiling tiles, walls or floors, due to the reflection and absorption of frequency components.
Current detectors either have no sensitivity adjustment or a sensitivity adjustment which is set by an installer. When an installer manually adjusts the sensitivity, the adjustment can still be incorrect. To adjust the level of sensitivity of the detector, an installer needs to open the detector each time the level must be changed. In practice, the sensitivity adjustment occurs multiple times, requiring the installer to manually adjust the sensitivity each time by changing a setting inside the detector. With the current setting method, the environmental characteristics are not optimized for detection, which results in false alarms.
Accordingly, there is a need for an apparatus and method for calibrating a glass break detection system that will reduce false alarms and optimize a detection range for its environment.